The present invention relates generally to bipolar transistors and fabrication methods, and more particularly, to a high-voltage bipolar transistor that employs field-terminated bond-pad electrodes and a method of fabricating same.
Bipolar transistor technology is well known, dating back to the invention of the germanium junction transistor in 1948 by Shockley, Bardeen and Brattain. In 1951, Shockley proposed the use of the abrupt heterojunction as an emitter-base junction in a bipolar transistor, which is disclosed in U.S. Pat. No. 2,569,347. Since that time, the fabrication of both single and double-heterojunction bipolar transistors in gallium arsenide (GaAs) and indium phosphide (InP) has received considerable attention. Description to such transistors may be found, for example, in "Fabrication of Self-Aligned GaAs/AlGaAs and GaAs/InGaP Microwave Power Heterojunction Bipolar Transistors", by J. Ren, et al, J. Vac. Sci. Technol. B. Vol. 12, No. 5, pp. 2916-2928, September, 1994, "Comparison of InGaP/GaAs Single- and Double-Heterojunction Bipolar Transistors with Carbon Doped Base", by A. W. Hanson, et al, IEEE Electron Device Letters, Vol. 14, No. 1, pp. 25-27, June, 1994, "High-Linearity Power X-Band GaInP/GaAs Heterojunction Bipolar Transistor", by W. Liu, et al, IEEE Electron Device Letters, Vol. 15, No. 6, pp. 190-192, June, 1994, "Fabrication and Characterization of High-Performance InP/InGaAs Double Heterojunction Bipolar Transistors", by K. Kurishima, et al, IEEE Transactions on Electron Devices, Vol. 41, No. 8, pp. 1319-1326, August, 1994, "60 Ghz AlInAs/GaInAs/InP DHBTs Grown by MOCVD+MBE", by W. E. Stanchina, et al, 1991 Tech. Dig., p VIA-6, and "InP-Based Heterojunction Bipolar Transistors: Performance Status and Circuit Applications", by P. M. Asbeck, et al, Paper MA. 1, presented at the Second International Conference on InP and Related Materials, Conf. Proc., pp. 2-5.
In addition to the above mentioned applications, there is also a current need for high-speed switching transistors with operating voltage in excess of 200 V, for example, for use in VHF resonant power converters. Until now, no device existed that could satisfy this need. Using silicon technology, high-voltage switching can be achieved at essentially audio frequencies, and high-speed switching can be achieved only at low-voltage. High-voltage switching devices of GaAs-based heterojunction bipolar transistors at VHF frequencies have been developed by the assignee of the present invention that have higher power gain and efficiency than the best available silicon devices. However, prior to the present invention, there has been no device structure that provides a highly reliable VHF switching transistor for resonant power supply applications that has an operating voltage in excess of 200 V.
The use of a field-plate and equipotential ring, such as are disclosed in "Effect of Surface Fields on the Breakdown Voltage of Planar Si p-n Junctions", by A. S. Grove, et al, IEEE Trans. 14 Electron Dev., ED-14, No. 3, pp. 157-162 (1967), and "Design Considerations for High-Voltage Overlap Annular Diodes", by D. S. Zoroglu, et al, IEEE Trans. Electron Dev., ED-19, No. 8, pp. 4-8, (1972) are well known for improving p-n junction breakdown voltage and reliability in silicon technology. However, these structures are concentric rings, and no mention is made in these papers regarding an overlapping configuration such as is employed in the present invention.
Accordingly, it is an objective of the present invention to provide for an improved high-voltage bipolar transistor and a method of fabricating same.